We are no strangers to rubber bands. And silica gel as the new favorite of the band material, often appears in the sports watch and diving watch. On the surface, the band is similar to the traditional rubber band, but seems to be different.
Silica gel is a large family, divided into inorganic silica gel and organic silicone two groups. Inorganic silica gel is a kind of highly active adsorption material, which is usually prepared by the reaction of sodium silicate and sulfuric acid and a series of post-treatment processes such as aging and acid-bubble. Its main ingredient is silica, and its structure is like a sponge. The interconnected pores constitute a capillary adsorption system with a large surface area, capable of absorbing and condensing moisture equal to 40% of its own weight, and therefore are mostly used as desiccant. Although inorganic silica gel is not used for making watch straps, it is often used in the care of the watch -- as long as the silica gel particles and water on the watch are placed in an airtight container, after a few hours, the water in the watch will all disappear.
Our daily use is more organic silica gel, it is divided into silicon rubber, silicon resin and silicon oil, is a special rubber in synthetic rubber. The commonly used material in the band is a small branch of the organic silicone family, the room temperature vulcanized silicone (RTV) in silicone rubber.
The raw materials of silicon rubber are silicon powder, methanol and hydrochloric acid. It is also called "liquid silica gel" because of its low molecular weight and its liquid state at room temperature. After the crosslinking agent and platinum catalyst are mixed in the liquid silica gel, they are then injected into the model. After a period of vulcanization reaction, they can be solidified and formed (it can be reacted at room temperature, so it is called vulcanized silicone rubber at room temperature, which can also be slightly heated to improve the reaction speed). And form the final product. Adding different additives can make the silicone materials have different specific gravity, hardness, strength, color and texture.
Silicon rubber has better high and low temperature resistance than pure organic rubber. Conventional rubber is frozen and crunchy in space, where the sun cannot reach it. As a space material developed silicon rubber, the biggest characteristic is not afraid of high temperature and can resist cold. Both at 300 ° C to 90 ° C under extreme conditions, it can be poised to keep its chemical structure, do not lose the original flexibility.
There is no bacterial growth compared to natural rubber. And its surface tension is very low, not easy to be soaked by sweat and rain deformation, with a strong waterproof corrosion. As a result, silicone rubber products in the natural environment of the mission life for decades.
Silicon rubber is not omnipotent, its tear resistance in rubber is a lower class. Therefore, the connection part between the silicon watch band and the metal ring is easy to cause small cracks due to larger external forces. Therefore, when using the silica gel band, it is necessary to pay attention to the connection part between the band and the metal ring, and do not pull hard. In addition, soft cloth is often used to clean the silica gel band, to remove some hard dust particles, to prevent its scratch on the surface of silica gel to produce small cracks, but also effectively extend the life of the band.
The method of identifying silica gel is more complex than that of ordinary rubber, and the infrared spectrum analysis can scientifically determine the varieties of corresponding materials by different absorption peaks on the spectrum. But for consumers it is only through the senses. Generally speaking, silica gel products are colorless and tasteless, and transparent when no pigments are added. If different dyes are added, black silica gel and colored silica gel can be obtained. But rubber products have more or less a taste. Natural rubber, on its own, has a protein taste, whereas rubber, which is made from sulphur, has a special taste. As for some people judging by the softness, it's not right to think that silicone feels softer than rubber. Because ordinary rubber or resin materials through different additives, the same as silicone products can be soft.